PHYSICAL EXTRACTION OF PROPIONIC ACID · Extraction of propionic acid was studied using different...

IJRRAS 3 (3) ● June 2010 Wasewar & al. ● Physical Extraction of Propionic Acid

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PHYSICAL EXTRACTION OF PROPIONIC ACID

Kailas L. Wasewar1*, Amit Keshav

2 & Seema

2

1 Department of Chemical Engineering, National Institute of Technology (NIT) Nagpur,

Maharashtra – INDIA 2 Department of Chemical Engineering, National Institute of Technology (NIT) Raipur,

Chhattishgarh -492010, INDIA

* Corresponding Author Email:[email protected]

ABSTRACT

Extraction of propionic acid was studied using different diluents (aliphatic hydrocarbons, aromatic hydrocarbons,

esters, alcohols and ketone). The data were presented in terms of distribution coefficient, partition coefficient (P)

and dimerization constants (D). The differences in degree of extraction of propionic acid by these diluents were

explained in terms of relative permittivity, dipole moment and ET values. The value of P and D shows that there is a

close relation between these values and the chemical nature of solvent. Attempts have been made to correlate diluent

DK with the physico-chemical parameters of the diluents chosen. However, no general correlation could be

found. So it is necessary to have an empirical parameter that should give assessment of solvation energy of the

solute and show the effect of intramolecular forces better. The parameters used in the study ET parameter. It is found

that higher the ET value of the solvent higher is the diluent

DK .Effect of temperature on P and D was also studied.

Diluents oleyl alcohol, ethyl acetate, MIBK, 1-decanol and 1-octanol were used for the study. In alcohols P was

found to increase with increase in temperature, however, for ethyl acetate and MIBK it decreases. ΔH and ΔS values

were also calculated for the physical extraction of carboxylic acids using 1-octanol. It can be seen that ΔH and ΔS

values were positive, thus the partitioning process is endothermic and is entropy driven process and the order of

system increases.

Keywords: Propionic acid, Extraction, Temperature, Partition coefficient, Dimerization constant

1. INTRODUCTION

Physical extraction involves the extraction of solute into inert non reacting hydrocarbons and substituted

hydrocarbons and is relatively free of complexities. Two factors need to be accounted to show the influence of

diluents on the extraction: (a) partial dissociation of the acids in aqueous phase and (b) dimerization in the

hydrocarbon phase. Another important parameter particularly in carbon bonded oxygen donor solvents is the water

of hydration (Kertes and King, 1986). High attraction of binding of the acid with the water molecules requires large

amount of solvent molecules so that they can compete with the water molecules that hydrate the acid at the interface.

There are number of ways by which solvents for physical extraction can be classified. On the basis of molecular

structure, they are classified as polar protic, dipolar aprotic and non-polar solvents.

Polar protic solvents: A polar protic molecule consists of a polar group OH and a non-polar tail.

Dipolar aprotic solvents: Dipolar aprotic molecules possess a large bond dipole moment (a measure of polarity of a

molecule chemical bond). They do not contain OH group.

Non-polar solvents: Electric charge in the molecules of non-polar solvents is evenly distributed; therefore the

molecules have low dielectric constant. Non-polar solvents are hydrophobic (immiscible with water). Non-polar

solvents are liphophilic as they dissolve non-polar substances such as oils, fats, greases.

On the basis of nature, solvents are classified as inorganic and organic solvents.

Inorganic solvents: The most popular inorganic (not containing carbon) solvents are water (H2O) and aqueous

solutions containing special additives (surfactants, detergents, pH buffers and inhibitors). Other inorganic solvents

are liquid anhydrous ammonia (NH3), concentrated sulfuric acid (H2SO4), sulfuryl chloride fluoride (SO2ClF).

Organic solvents: These are further subdivided into two types:

Oxygenated solvents: Oxygenated solvents are organic solvent, molecules of which contain oxygen. Oxygenated

solvents are widely used in paints, inks, pharmaceuticals, fragrance sectors, adhesives, cosmetics, detergents, food

industries. Examples of oxygenated solvents: alcohols, glycol ethers, methyl acetate, ethyl acetate, ketones, esters,

and glycol esters.

Hydrocarbon solvents: Molecules of hydrocarbon solvents consist only of hydrogen and carbon atoms. They are

classified as

http://www.substech.com/dokuwiki/doku.php?id=hydrocarbon_solvents&DokuWiki=94dd81c537c2e6c35baf53e557776406


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Aliphatic solvents:

Aliphatic solvents are having straight chain structure. Examples include hexane, kerosene, heptane etc.

Aromatic solvents:

Molecules of pure aromatic solvents have benzene ring structure. Examples of pure aromatic solvents are benzene,

toluene and xylene.

Halogenated solvents

Halogenated solvent is an organic solvent, molecules of which contain halogenic atoms: chlorine (Cl), fluorine (F),

bromine (Br) or iodine.

Natural solvents

There are solvents which are obtained from natural products like sunflower seeds (sunflower oil), coconut (coconut

oil) etc.

Table 1: Partition and dimerization constants for extraction of different carboxylic acid using different diluents.

Diluent P D (l/mol) Diluent P D (l/mol)

nitrobenzene 0.524 -- chloroform 0.110 30

15 % chloroform + n-heptane 0.008 0.007 nitrobenzene 0.160 11

n-hexane 0.005 9000 diethyl ather 1.750 0.1

chlorohexane 0.006 6500 diisopropyl ether 0.800 0.5

benzene 0.043 190 MIBK 2.150 --

toluene 0.034 230 cyclohexanone 3.300 --

xylene 0.030 310 n-butanol 3.200 --

carbon tetrachloride 0.015 940 n-pentanol 2.950 --

Kertes and King, (1986) presented the extraction of propionic acid using different diluents and the results have been

reported in Table 1. The values of partition, dimerization and overall distribution coefficients have been stated. Very

limited studies on physical extraction of propionic acid (that too scattered), can be found in literature. In view of

this, in this chapter, the extraction of propionic acid was studied using different diluents: (a) aliphatic hydrocarbons:

heptane, hexane, paraffin liquid, petroleum ether and kerosene; (b) aromatic hydrocarbons: benzene, toluene; (c)

esters: butyl acetate, ethyl acetate; (d) alcohols: 1-octanol, 2-octanol, 1-decanol, 1-dodecanol, oleyl alcohol; and (e)

ketone: MIBK. The data were presented in terms of distribution coefficient, partition coefficient and dimerization

constants.

2. THEORY

Carboxylic acids mainly exist as dimmers in the organic phase owing to strong intermolecular hydrogen bonding,

especially in non polar or slightly polar diluents. On the contrary, in the aqueous phase, they existed as monomers

because of the intermolecular hydrogen bonding between the acids is destroyed owing to their preferential hydrogen

bonding with the water molecules. At the pH less than the pKa values of acid, the acid can be assumed to be

transferred into organic solvent by the following mechanism:

i) Ionization of the acid in the aqueous phase:

[HA]aq ↔ H+ + A

- (1)

KHA = [H+][A

-] / [HA] (2)

ii) Partition of the undissociated molecular acid between the two phases, aqueous (aq) and organic (org):

[HA]aq↔ [HA]org (3)

P = [HA ]org / [ HA]aq (4)

iii) Dimerization of the acid in the organic phase:

2[HA]org ↔ [HA]2org (5)

D = [HA]2,org / [ HA]2 org (6)

Overall distribution coefficient is defined as the ratio of total (analytical) concentration of acid in all its forms (by

partition, dimmers and as complexes) in organic phase and total (analytical) concentration of all its existing forms

(dissociated and undissociated) in aqueous raffinate (Keshav et al., 2009f). It includes the effects like ionic strength,

nature of ion concentration of H+ etc. of solution constituents. For physical extraction, distribution coefficient can be

defined as:

aqHA

aq

2

diluent

D]H/[1

[HA]2

K

DPPK (7)


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Under the experimental condition that pH of the aqueous solution was smaller than pKa of the acid (4.88) (Playne,

1985) and since, dilute solutions of acids were taken (0.05 – 0.4 kmol/m3), effect of the acid dissociation was

negligibly small. Thus the denominator term can be safely neglected and equation (7) can be modified to get

aq

2diluent

D ]HA[2 DPPK (8)

King and King (1986) stated that the values of P and D obtained by above equation may be misleading on account

of two reasons: first, the degree of hydration of acid in organic phase is unknown and varies with concentration and

second; the partition process defined by equation (7) requires quantities that measure the activity of the distribuend;

the activity coefficient of the species in both phases and partition coefficient values in mol fraction scale.

3. EXPERIMENTAL

3.1. Chemicals

Propionic acid and the diluents: heptane, hexane, petroleum ether, paraffin liquid, kerosene, benzene, toluene,

hexanol, 1-decanol, 1-octanol, 2-octanol, 1-dodecanol, oleyl alcohol, MIBK, butyl acetate, ethyl acetate are of

technical grade and were used as supplied by suppliers. The various specifications of the diluents are given in Table

2. Distilled water was used to prepare the solutions of various concentrations of propionic acid solutions. NaOH

used for titration is of analytical grade and was supplied by Ranbaxy, India. For the standardization of the NaOH,

oxalic acid (99.8%) was obtained from s. d. Fine-Chem. Ltd., India. Phenolphthalein solution (pH range 8.2 to 10.0)

was used as indicator for titration and was obtained from Ranbaxy, India. The initial aqueous acid concentrations

range ([HA]o) of (0.05 to 0.4) kmol/m3

were used. Low concentration was used because propionic acid concentration

in the fermentation broth is not greater than 0.5 kmol/m3 (Lewis and Yang, 1992).

Table 2: List and specification of various diluents used for the extraction of propionic acid.

Solvents MW Molecular formula Make Purity (%)

Hexane 86.18 C6H14 Ranbaxy Ltd., India 99.5

n-Heptane 100.2 C7H16 Ranbaxy Ltd., India 99.0

Petroleum ether 87-114 - s. d. Fine Chem. Ltd., India 99.0

Kerosene 170 - - -

Benzene 78.11 C6H6 Ranbaxy Ltd., India 99.0

Toluene 92.17 C6H5CH3 Nice Ltd., India 99.0

Paraffin liquid (L) - - RFCL Ltd., India 99.0

Paraffin liquid (H) - - RFCL Ltd., India 99.0

Butyl acetate 116.16 C6H12O7 SRL Ltd., India 98.0

Ethyl acetate 88.106 C4H8O2 RFCL Ltd., India 99.0

MIBK 100.16 CH3COC4H9 Ranbaxy Ltd., India 99.0

1-hexanol 102.2 C6H14O Himedia India ltd. 99.0

1-Octanol 130.28 CH3(CH2)7 OH Himedia India ltd. 98.0

2-octanol 130.3 C8H180 Himedia India ltd. 99.0

1-Decanol 158.29 CH3(CH2)9OH Himedia India ltd. 98.0

Dodecanol 186.34 CH3(CH2)11 OH Acros, USA 99.0

Oleyl alcohol 268.49 C18H36O s. d. Fine Chem. Ltd., India 98.0

3.2. Procedure

Extraction experiments involve shaking of equal volumes of aqueous and organic phases for 12 h at constant

temperature (305 K) in orbital shaking incubator (Metrex Scientific Instruments (P). Ltd. India) at 190 rpm,

followed by settling of the mixture for at least 2 h at the same temperature in separating funnels maintained at that

temperature in an incubator. Aqueous phase pH was measured by an Orion 3 star pH meter (Thermo Electro

Corporation). Aqueous phase acid concentration was determined by titration with sodium hydroxide solution (0.02

N). The acid content in the organic phase was determined by a mass balance.

4. RESULTS AND DISCUSSION

Figures 1(a – d) show the physical equilibria for extraction of propionic acid using aliphatic and aromatic

hydrocarbons (hexane (Keshav et al., 2008b,c), , heptane (Keshav et al., 2008b,c,d; 2009a,c),, benzene (Keshav et


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al., 2008b), toluene (Keshav et al., 2008b; 2009a), long chain aliphatic hydrocarbons mixture (paraffin liquid light

(Keshav et al., 2008b,c), paraffin liquid heavy (Keshav et al., 2008b), petroleum ether (Keshav et al., 2008b,d,f;

2009a,c), kerosene), oxygenated diluents (ethyl acetate (Keshav et al., 2008d, 2009d), butyl acetate (Keshav et al.,

2008b), methyl iso butyl ketone (Keshav et al., 2009h,e,f) and alcohols (hexanol (Keshav et al., 2009h), 1-octanol

(Keshav et al., 2008a), 2-octanol (Keshav et al., 2009d), 1-decanol (Keshav et al., 2009c,d,f,h), do decanol (Keshav

et al., 2008b), oleyl alcohol (Keshav et al., 2008d; 2009b)) respectively. Extraction was found to follow the trend

alcohols > oxygenated diluents > aromatic hydrocarbons > aliphatic hydrocarbons > long chain aliphatic

hydrocarbons mixture. This suggests that alcohols and oxygenated diluents are most effective in physical extraction

of propionic from dilute solutions. With increase in acid concentration, diluent

DK was found to be nearly constant for

alcohols and ketone, however, for aliphatic and aromatic hydrocarbons there is abrupt increase in diluent

DK values at

high acid concentration (Table 3).

The reason of the behavior can be explained as follows. The extent of hydration of the acid and energy of the bond

to water molecules are the two factors that affect extractability. Aliphatic hydrocarbons (hexane, heptane, kerosene,

petroleum ether etc.) have very low solubility in water, so they behave close to ideality in term of volume changes

when propionic acid at low concentration partitions between them. To obtain complete miscibility in the phases,

very high concentration of propionic acid is required. At high acid content i.e. in water deficient situation, the

solvation sheath around propionic acid is composed of both water and solvent molecules, thus making the solute

species more like organic solvent. Thus appearance of abrupt value of diluent

DK at higher acid concentration was

observed.

Aliphatic and aromatic hydrocarbons (hexane, heptane, benzene, toluene, paraffin liquid light, paraffin liquid heavy,

petroleum ether and kerosene) are apolar aprotic solvents and are characterized by low relative permittivity(ε), low

dipole moment, low ET value and are unable to act as an hydrogen bond donor. So these solvents interact only slightly

with the acid since only the non specific directional, induction and dispersion forces are operating giving very low diluent

DK values. Esters: butyl acetate, ethyl acetate, and ketone: MIBK on the other hand are dipolar aprotic solvents and

have large relative permittivity (ε), dipole moment, and ET values. Though these solvents do not act as hydrogen bond

donors since C-H bonds are not sufficiently polarized, still they provide high diluent

DK values due to presence of ion

electron pairs. Anion solvation occurs mainly by ion-dipole and ion-induced dipole forces. The latter are important for

large, polarizable, soft anions, with low charge density. Therefore although these solvents tend to be poor anion

solvators, they are usually better, the larger and softer the anion. Alcohols, considered as protic solvents, contain

hydrogen atoms bound to electronegative element O (-O-H), are hydrogen bond donors. Their relative permittivity (ε)

and ET value are large, indicating them to be strongly polar. Thus they provide high diluent

DK values since they are good

anion solvators due to their hydrogen bonding ability. The tendency becomes more pronounced as the charge density

(ratio of charge to volume) of the anion to be solvated increases. Further alcohols are capable of being both acceptors

and donors, as are the acids; give the highest diluent

DK followed by purely basic solvents such as ethers and ketones.

Table 3 shows the physical equilibria for extraction of propionic acid using different solvents. Partition (P) and

dimerization (D) coefficients were also evaluated. Mutual solubility between an aqueous solution and a given solvent at

fixed temperature is affected by the nature of distribuend and its total concentration in the system. Propionic acid is a

weak carboxylic acid and mutual solubility’s can cause dramatic volume changes particularly at higher acid

concentrations. Mutual solubility increases the volume of organic layer at the expense of that of aqueous phase in

equilibrium and it increases with increase in acid concentration. Another important thing to be mentioned here is that the

values of P and D are not the values obtained by pure water and solvent phases. These are obtained by mutual saturation

of the two phases, obtained by equilibrium between two mutually saturated phases rather that between pure water and

solvent. However since only dilute concentrations of acid were taken in study (0.05 – 0.4 kmol/m3), there is low

solubility of the phase and thus there is not much variance between these values and values from pure media.


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0

0.04

0.08

0.12

0 0.1 0.2 0.3 0.4

[HA

]org

(km

ol/m

3)

[HA]aq (kmol/m3)

n-heptane

Hexane

benzene

toluene

Figure 1 (a): Physical extraction equilibrium

curves for extraction of propionic acid using

different diluents (heptane, hexane, benzene and

toluene)

0

0.03

0.06

0.09

0.12

0 0.1 0.2 0.3 0.4 0.5

[HA

]org

(km

ol/m

3)

[HA]aq (kmol/m3)

paraffin liquid light

petroleum ether

paraffin liquid heavy

kerosene

Figure 1 (b): Physical extraction equilibrium


different diluents (paraffin liquid light, petroleum

ether, paraffin liquid heavy and kerosene)

0

0.1

0.2

0.3

0.4

0 0.1 0.2 0.3

[HA

]org

(km

ol/m

3)

[HA]aq (kmol/m3)

MIBK

ethyl acetate

butyl acetate

Figure 1 (c): Physical extraction equilibrium


different diluents (methyl isobutyl ketone (MIBK),

ethyl acetate and butyl acetate)

0

0.1

0.2

0.3

0.4

0 0.1 0.2 0.3

[HA

]org

(km

ol/m

3)

[HA]aq (kmol/m3)

1-octanol

2-octanol

oleyl alcohol

1-decanol

dodecanol

hexanol

Figure 1 (d): Physical extraction equilibrium


different diluents (1-octanol, 2-octanol, oleyl

alcohol, 1-decanol, 1-dodecanol and hexanol)

The values of P and D listed in Table 3 shows that there is a close relation between these values and the chemical

nature of solvent. Alcohols as already discussed, are capable of being both acceptors and donors, thus expected to

provide highest partitions coefficients (P). The D values on the other hand are very small or negligible due to

stronger solute-solvent hydrogen bond in comparison to solute-solute bond, which would have lead to form dimmers.

Thus, it can be ascertained that the values of P and D are inversely proportional to each other.

A number of studies have been made to carry out the influence of diluents on extraction equilibrium. Some of

them quote a relationship between the distribution coefficient and other physico-chemical diluent parameters such as

dielectric constant, dipole moment etc (Diamond, 1936; Kozime, 1987). In presented studies, attempts have been

made to correlate diluent

DK with the physical parameters of the diluents chosen. The various physical properties of

diluents used for comparison are given in Table 4. It can be found that higher diluent

DK values are obtained with

higher dipole moment, higher dielectric constant, and lower log P values of the diluent except for alcohols. Further

among the diluents of similar type specific observation can be defined. Among aliphatic hydrocarbons (hexane and

heptane), it can be found that lower the molecular weight, lower the density and higher the refractive index of the

solvent, higher is the diluent

DK value. Among benzene and toluene, introduction of side chain in toluene caused

increase in diluent

DK value. Alcohols show an arbitrary behavior. diluent

DK was found to increase with increase in

chain length from 1-octanol and 1-decanol when the OH group is at first carbon atom, however when OH is at

second carbon atom (2-octanol) the values were much higher than the above two diluents (1-octanol and 1-decanol).


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Lower alcohol 1-hexanol was found to give extremely high value of diluent

DK in comparison to all other alcohols. The

probable reason for that may be the high solubility is water of the former (0.59 g/100 ml at 20°C). Another alcohol,

oleyl alcohol, because of its high viscosity failed to extract the acid physically thus yielding very low diluent

DK

values, much lower than even the active diluents.

Table 3: Physical equilibria of extraction of propionic acid using different diluents

Diluent [HA]o [HA]aq [HA]org KDdiluent E% pHaq P D

kmol/m3 kmol/m3 kmol/m3 m3/kmol

hexane

0.05 0.044 0.006 0.134 11.80 3.17

0.045 53.802

0.1 0.084 0.016 0.187 15.72 3.01

0.15 0.139 0.011 0.078 7.23 2.89

0.2 0.188 0.012 0.063 5.92 2.82

0.3 0.278 0.022 0.078 7.23 2.73

0.4 0.352 0.048 0.137 12.05 2.68

n heptane

0.05 0.056 0.006 0.106 9.61 3.11

0.076

24.710

0.1 0.104 0.009 0.087 7.99 2.96

0.15 0.139 0.011 0.077 7.16 2.89

0.2 0.196 0.031 0.160 13.77 2.81

0.3 0.258 0.042 0.162 13.96 2.75

0.4 0.342 0.058 0.168 14.38 2.69

paraffin

liquid(L)

0.05 0.047 0.004 0.085 7.86 3.15

0.051 18.454

0.1 0.096 0.004 0.043 4.10 2.98

0.15 0.141 0.009 0.062 5.81 2.89

0.2 0.196 0.015 0.077 7.12 2.81

0.3 0.279 0.021 0.076 7.09 2.73

0.4 0.347 0.053 0.151 13.14 2.68

paraffin

liquid(H)

0.05 0.048 0.002 0.034 3.33 3.15

0.050 -

0.1 0.096 0.004 0.042 4.00 2.98

0.15 0.143 0.007 0.047 4.44 2.88

0.2 0.193 0.007 0.034 3.33 2.81

0.3 0.298 0.002 0.007 0.67 2.72

0.4 0.398 0.002 0.004 0.42 2.65

petroleum ether

0.05 0.053 0.002 0.038 3.65 3.12

0.009 5595.945

0.1 0.095 0.005 0.049 4.64 2.98

0.15 0.126 0.024 0.190 15.96 2.91

0.2 0.180 0.020 0.110 9.92 2.83

0.3 0.241 0.059 0.246 19.74 2.76

0.4 0.314 0.086 0.275 21.56 2.71

kerosene

0.05 0.048 0.002 0.034 3.33 3.15

0.170 -

0.1 0.093 0.007 0.071 6.67 2.98

0.15 0.133 0.017 0.125 11.11 2.90

0.2 0.162 0.038 0.237 19.17 2.86

0.3 0.251 0.049 0.195 16.33 2.74

0.4 0.393 0.007 0.017 1.67 2.66


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benzene

0.05 0.044 0.006 0.134 11.80 3.17

0.031 400.110

0.1 0.086 0.014 0.160 13.76 3.00

0.15 0.132 0.018 0.134 11.80 2.90

0.2 0.172 0.028 0.160 13.76 2.84

0.3 0.254 0.046 0.182 15.39 2.75

0.4 0.311 0.089 0.286 22.21 2.71

toluene

0.05 0.046 0.004 0.087 7.99 3.13

0.084 77.844

0.1 0.090 0.010 0.111 10.00 2.99

0.15 0.122 0.028 0.230 18.73 2.92

0.2 0.139 0.061 0.439 30.46 2.69

0.3 0.220 0.080 0.363 26.64 2.78

0.4 0.288 0.112 0.389 28.00 2.73

butyl acetate

0.05 0.023 0.028 1.222 55.00 3.35

1.468 -

0.1 0.038 0.063 1.667 62.50 3.21

0.15 0.063 0.088 1.400 58.33 3.08

0.2 0.080 0.120 1.500 60.00 3.02

0.3 0.128 0.173 1.353 57.50 2.91

0.4 0.165 0.235 1.424 58.75 2.85

ethyl acetate

0.05 0.017 0.033 1.914 65.68 3.42

2.391 0.368

0.1 0.028 0.072 2.529 71.66 0.00

0.15 0.042 0.108 2.551 71.84 3.18

0.2 0.054 0.146 2.726 73.16 3.12

0.3 0.081 0.219 2.724 73.15 0.00

0.4 0.105 0.295 2.820 73.82 2.96

MIBK

0.05 0.037 0.013 0.347 25.75 3.22

0.670 4.283

0.1 0.054 0.046 0.865 46.38 3.12

0.15 0.069 0.081 1.182 54.17 3.06

0.2 0.088 0.112 1.273 56.00 3.00

0.3 0.121 0.179 1.479 59.67 2.92

0.4 0.157 0.243 1.552 60.81 2.86

hexanol

0.05 0.013 0.054 4.140 80.54 3.12

4.505 -

0.1 0.025 0.108 4.261 80.99 2.95

0.15 0.041 0.160 3.950 79.80 2.86

0.2 0.055 0.212 3.860 79.42 2.84

0.3 0.080 0.254 3.176 76.05 2.75

0.4 0.093 0.308 3.311 76.80 2.71

1- octanol

0.05 0.020 0.030 1.500 60.00 3.38

1.735 0.118

0.1 0.039 0.061 1.572 61.12 3.20

0.15 0.056 0.094 1.700 62.97 3.11

0.2 0.078 0.122 1.572 61.12 3.03

0.3 0.107 0.193 1.813 64.45 2.95

0.4 0.154 0.246 1.590 61.39 2.87


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2-octanol

0.05 0.015 0.035 2.306 69.75 3.46

2.310 0.025

0.1 0.030 0.070 2.306 69.75 3.27

0.15 0.047 0.103 2.209 68.83 3.16

0.2 0.063 0.137 2.162 68.38 3.08

0.3 0.088 0.212 2.409 70.67 3.00

0.4 0.124 0.276 2.232 69.06 2.92

1 decanol

0.05 0.021 0.029 1.397 58.27 3.37

1.406 -

0.1 0.039 0.061 1.546 60.73 3.20

0.15 0.052 0.098 1.865 65.09 3.13

0.2 0.147 0.053 0.358 26.37 2.88

0.3 0.099 0.201 2.030 67.00 2.97

0.4 0.133 0.267 2.018 66.86 2.90

dodecanol

0.05 0.020 0.030 1.500 60.00 3.38

1.405 -

0.1 0.044 0.056 1.273 56.00 3.17

0.15 0.064 0.086 1.344 57.33 3.08

0.2 0.087 0.113 1.299 56.50 3.00

0.3 0.135 0.165 1.222 55.00 2.90

0.4 0.185 0.215 1.162 53.75 2.82

oleyl alcohol

0.05 0.028 0.023 0.818 45.00 3.29

0.702 0.682

0.1 0.059 0.041 0.691 40.88 3.10

0.15 0.083 0.068 0.818 45.00 3.01

0.2 0.117 0.083 0.711 41.56 2.93

0.3 0.162 0.138 0.849 45.92 2.85

0.4 0.217 0.183 0.841 45.69 2.79

The above results prove that the extractability of the acid may be correlated to some extent with the physico-

chemical properties of the solvents, yet no general correlation could be found. The reason for that may be that the

effect of diluent is determined by the ratio of the contribution of the solvation of acid to the free energy of extraction.

Solvation is a complex mechanism and depends on different kinds of intermolecular forces which cannot be merely

stated in terms of the above physicochemical parameters. However, diluent

DK can be proposed to depend on the

mechanism of extraction and nature of diluents used. Rozen (1962) correlated the influence of the diluent on the

extraction with zero activity coefficients. However, the correct expression for effect of diluent on extraction

equilibrium, requires paying attention on the method of expressing the distribution coefficient. In order to avoid the

complications of effect of molecular and specific weights of the diluents, it is better to use mole fraction instead of

activity to express the influence of diluent. Further it is necessary to extrapolate the distribution coefficient to

extremely dilute solutions in order to eliminate the concentration activity coefficients.

Assuming the mutual solubility of water and diluent to be negligible, diluent

DK can be expressed as

o

diluent

Do

diluent

D logloglog/ CKorCK (9)

Where, o is the zero activity coefficient of the acid in the solvent phase and C is a constant. The zero activity

coefficients specifies the transfer energy of a substance passing from an infinitely dilute solution into the pure state

and is determined by the energy of the crystal lattice of the distributed solute, less the energy of its solvation by the

solvent. Since the energy of the crystal lattice for a given distributed solute is constant, diluent

Dlog K should be a

linear function of its solvation energy. So it is necessary to have an empirical parameter that should give assessment

of solvation energy of the solute and show the effect of intramolecular forces better. The parameters most frequently

used are Z parameter (Kosower , 1958) which account for the influence of the solvent on the position of the charge

transfer band in the spectrum of alkylpyridine iodide, and the ET parameter (Dimroth, 1963) which is based on the

absorption spectrum of pyridinium-N-phenol-betaine. In these co-ordinates, which are in satisfactory agreement with

each other, the position of the charge transfer band (kcal/mol) is used as the characteristic of the solvent. ET was used


298

here to describe the effect of solvent polarity on diluent

DK since it has been determined for number of solvents. Table

5 shows the diluent

DK values against the ET values of the corresponding solvents. It is found that higher the ET value

of the solvent higher is thediluent

DK . Some discrepancy arises in the case of extraction using ethyl acetate and oleyl

alcohol, where high water solubility and highly viscous nature of respective diluents can be the cause of their

abruptly higher and abruptly lower diluent

DK values obtained, respectively.

Table 4: Various physicochemical properties of diluents chosen in extraction of propionic acid.

Solvents MW molecular

structure

BP

oC

MP

oC

Solubility

in water

ρ

g/cm3 RI

μ

cP

ε

Log

(P) DM ET

Hexane 86.18 C6H14 68.7 -95

immiscible 0.671 1.3723 0.294 2.0 3.70 0.08 31.0

n-Heptane 100.2 C7H16 98 -90.61

immiscible 0.6795 1.3851 0.386 1.9 4.66 0 31.1

Petroleum

ether 87-11 -- 20-75

-73 immiscible -- -- -- -- -- -- --

Kerosene 170 -- 147 -73

Insoluble 0.817 1.443 -- 1.8 -- -- --

Benzene 78.11 C6H6 80.9 5.5

1.79 g/l 0.873 1.4979 0.652 2.3 2.13 0 34.3

Toluene 92.17 C6H5CH3 110.6 -93 0.053g/100

ml 0.865 1.497 0.590 2.379 2.69 0.36 33.9

Paraffin liquid (L)

-- -- -- -- --

0.820-0.880

1.473-1.483

-- 1.9-2.5

-- -- --

Paraffin

liquid (H) -- -- --

-- --

0.875-

0.905 -- -- -- -- -- --

Butyl acetate 116.16 C6H12O7 126 -78 0.7

g/100ml 0.879 1.394 0.832 5.1 1.82 1.84 38.5

Ethyl acetate 88.10 C4H8O2 77.6 -84

very high 0.894 1.3704 0.426 6.0 0.73 1.88 38.1

MIBK 100.16 CH3COC4H

9

114-117

-84.7 1.91 g/100ml

0.829 1.395 0.58 12.4 (62 oF)

-- 4.2 39.4

1-hexanol 102.2 C6H14O 151.8 -52 0.59g/100

ml 0.814 -- -- 13.3 2.03 1.66 48.8

1-Octanol 130.28 CH3(CH2)7

OH 195

-15.5 0.30mg/l 0.827 1.4295 8.925 10.3 3.00 1.71 48.3

2-octanol 130.3 C8H180 178.5 -38.6 0.096 ml

/100 ml 0.820 1.424 -- -- 2.72 -- 48.2

1-Decanol 158.29 CH3(CH2)9

OH 230

7 0.37g/100

ml 0.827 1.4295 8.925 8.1 4.23 -- 48.1

Dodecanol 186.34 CH3(CH2)11

OH 260-262

24 immiscible 0.831 1.4413 -- 6.5 -- -- 47.5

Oleyl

alcohol 268.49 C18H36O

330 -

360

13-19 insoluble

0.845 -

0.855 1.461 -- -- -- -- 49.0

BP: boiling point; MP: melting point; RI: refractive index; ρ: density of pure liquid; μ: viscosity; ε: dielectric

constant; log(P): octanol water partition coefficient; DM: Dipole moment

Table 5 Effect of diluent

DK on ET parameter.

Diluent ET KDdiluent

Diluent ET KDdiluent

hexane 31.0 0.063 dodecanol 47.5 1.299

n heptane 31.1 0.160 1 decanol 47.7 1.865

benzene 34.3 0.160 1- octanol 48.1 1.572

toluene 33.9 0.363 2-octanol 48.2 2.162

ethyl acetate 38.1 2.726 hexanol 48.8 3.780

MIBK 39.4 1.273 oleyl alcohol 49.0 0.711

butyl

acetate 38.5 1.500

Attempts were also made to correlate P and D values with the physico-chemical properties however no

generalization could be made. It may be stated that alcohols (protic solvents) and esters and ketones (dipolar aprotic

solvents) have higher P values and lower D values in comparison to aliphatic and aromatic hydrocarbons. The reason

of this is the improved solvation of the acid by hydrogen bonding in case of alcohols and ion pair interactions in case


299

of esters and ketones. Kertes and King (1986) correlated partition coefficient with the interfacial tension of the

solvent-water pair. The plot of log P versus interfacial tension was found to yield a straight line for solvents having

interfacial tension value greater than 9 dynes/cm. The relation was valid in view of lipophilic-hydrophilic balance in

the character of propionic acid.

Table 6: Effect of temperature on partition (P) and dimerization (D) coefficients for extraction of propionic acid using

different diluents.

Diluent Temp.

K

[HA]o

kmol/m3

[HA]aq

kmol/m3

[HA]org

kmol/m3

KDdiluent

E% pHaq P D

m3/kmol

ethyl

acetate

305

0.05 0.017 0.033 1.914 65.68 3.42

1.536 2.626 0.1 0.042 0.058 1.367 57.76 3.18

0.2 0.054 0.146 2.726 73.16 3.12

0.4 0.105 0.295 2.820 73.82 2.96

313

0.05 0.021 0.029 1.431 58.86 3.37

1.358 1.752 0.1 0.038 0.062 1.652 62.29 3.21

0.2 0.070 0.130 1.846 64.86 3.05

0.4 0.127 0.273 2.153 68.29 2.91

333

0.05 0.022 0.028 1.308 56.67 3.36

1.277 0.474 0.1 0.040 0.060 1.500 60.00 3.20

0.2 0.095 0.105 1.105 52.50 2.98

0.4 0.150 0.250 1.667 62.50 2.87

MIBK

305

0.05 0.029 0.022 0.754 43.00 3.28

0.707 10.550 0.1 0.044 0.057 1.299 56.50 3.17

0.2 0.075 0.125 1.667 62.50 3.04

0.4 0.132 0.268 2.030 67.00 2.90

313

0.05 0.048 0.002 0.042 4.00 3.15

0.077 668.378 0.1 0.072 0.028 0.389 28.00 3.05

0.2 0.105 0.095 0.913 47.71 2.96

0.4 0.166 0.234 1.406 58.43 2.85

333

0.05 0.048 0.002 0.034 3.33 3.15

0.011 37182.645 0.1 0.065 0.035 0.538 35.00 3.07

0.2 0.100 0.100 1.000 50.00 2.97

0.4 0.163 0.237 1.449 59.17 2.85

1-decanol

305

0.05 0.021 0.029 1.397 58.27 3.37

1.390 1.433 0.1 0.039 0.061 1.546 60.73 3.20

0.2 0.147 0.053 0.358 26.37 2.88

0.4 0.133 0.267 2.018 66.86 2.90

313

0.05 0.021 0.029 1.431 58.86 3.37

1.404 0.400 0.1 0.041 0.059 1.431 58.86 3.19

0.2 0.077 0.123 1.593 61.43 3.03

0.4 0.153 0.247 1.622 61.86 2.87

333

0.05 0.018 0.032 1.727 63.33 3.40

1.685 0.073 0.1 0.037 0.063 1.727 63.33 3.22

0.2 0.077 0.123 1.609 61.67 3.03

0.4 0.143 0.257 1.791 64.17 2.88

Oleyl

alcohol

305

0.05 0.028 0.023 0.818 45.00 3.29

0.743 0.369 0.1 0.059 0.041 0.691 40.88 3.10

0.2 0.117 0.083 0.711 41.56 2.93

0.4 0.217 0.183 0.841 45.69 2.79

313 0.05 0.024 0.026 1.083 52.00 3.33 0.751 0.354


300

0.1 0.048 0.052 1.083 52.00 3.15

0.2 0.101 0.099 0.977 49.43 2.97

0.4 0.195 0.205 1.047 51.14 2.81

323

0.05 0.027 0.023 0.823 45.14 3.29

0.759 0.253 0.1 0.055 0.045 0.823 45.14 3.12

0.2 0.117 0.083 0.716 41.71 2.93

0.4 0.216 0.184 0.852 46.00 2.79

333

0.05 0.027 0.023 0.882 46.86 3.30

0.972 0.218 0.1 0.046 0.054 1.161 53.71 3.16

0.2 0.101 0.099 0.977 49.43 2.97

0.4 0.190 0.210 1.102 52.43 2.82

2-octanol

305

0.05 0.015 0.035 2.306 69.75 3.46

2.289 - 0.1 0.030 0.070 2.306 69.75 3.27

0.2 0.063 0.137 2.162 68.38 3.08

0.4 0.124 0.276 2.232 69.06 2.92

313

0.05 0.014 0.036 2.646 72.57 3.48

3.522 - 0.1 0.027 0.123 4.469 81.71 3.29

0.2 0.062 0.138 2.241 69.14 3.09

0.4 0.117 0.283 2.431 70.86 2.93

333

0.05 0.013 0.037 2.750 73.33 3.49

3.835 - 0.1 0.025 0.125 5.000 83.33 3.32

0.2 0.058 0.142 2.429 70.83 3.10

0.4 0.110 0.290 2.636 72.50 2.95

1-octanol

298

0.05 0.014 0.036 2.472 71.20 3.47

2.391 0.391 0.1 0.056 0.144 2.571 72.00 3.11

0.2 0.080 0.220 2.750 73.33 3.02

0.4 0.104 0.296 2.846 74.00 2.96

308

0.05 0.015 0.035 2.378 70.40 3.46

2.918 0.212 0.1 0.051 0.149 2.906 74.40 3.13

0.2 0.076 0.224 2.927 74.53 3.03

0.4 0.104 0.296 2.846 74.00 2.96

318

0.05 0.012 0.038 3.054 75.33 3.51

3.022 0.075 0.1 0.050 0.150 3.004 75.03 3.14

0.2 0.073 0.227 3.123 75.74 3.05

0.4 0.096 0.304 3.158 75.95 2.98

328

0.05 0.014 0.036 2.682 72.84 3.49

2.890 0.051 0.1 0.050 0.150 3.017 75.10 3.14

0.2 0.077 0.223 2.898 74.35 3.03

0.4 0.100 0.300 2.991 74.94 2.97

Effect of temperature on P and D was also studied (Keshav et al., 2009b,d). Diluents oleyl alcohol, ethyl acetate,

MIBK, 1-decanol and 1-octanol were used for the study. 1-octanol has been used as diluent for particular

applications in the field of environmental and medicinal industry. 1-octanol/water partition coefficient (Pow), which is

the quantitative parameter for accessing the interaction between aqueous phase and organic phase, is one of the most

important parameters employed for estimating a chemical's environmental fate and toxicity. Table 6 shows the effect

of temperature on physical extraction of propionic acid using ethyl acetate, MIBK, 1-octanol, 1-decanol and oleyl

alcohol.

In alcohols P was found to increase with increase in temperature, however, for ethyl acetate and MIBK it decreases.

None of diluents except MIBK have significant D values. Considering the particular significance of 1-octanol/water

partition coefficient (Pow), the thermodynamics of extraction was studied. For the physical extraction of carboxylic

acids using 1-octanol, the changes in Gibbs free energy function (ΔG) of interaction between acid and biofilm

indicating the various interactions in the partitioning process of acid transferring from water to lipid phase and thus

judge the spontaneity of partition was calculated from the following equation

ΔG = ΔH - T ΔS (10)


301

where ΔH and ΔS are enthalpy and entropy of partition process of acid transferring from water phase to lipid phase.

ΔG is related to diluent/water partition coefficient as

ΔG = -2.303 RT log P (11)

where R is universal gas constant and T is temperature in K. Combining equations (10) and (11)

R

S

RT

HP

303.2303.2log

(12)

Thus, the plot of log P versus 1/T would give the values of ΔH and ΔS. ΔH and ΔS values were calculated as, 5.866

kJ/mol and 27.363 J/mol K. It can be seen that ΔH is positive, thus the partitioning process is endothermic. The

reason of this being that the interaction between acid and diluents is less powerful than that between acid and water

molecule owing to electrostatic force, hydrogen bond and hydrophobic interaction etc. So the energy was needed to

break the old bonds and form new bonds. ΔS value for the extraction of propionic acid is also positive, thus the

partitioning process is entropy driven process and the order of system increases.

CONCLUSIONS

Physical extraction of propionic acid using different diluents was studied. The following conclusion can be made:

1. Extraction was found to follow the trend alcohols > oxygenated diluents > aromatic hydrocarbons > aliphatic hydrocarbons >

long chain aliphatic hydrocarbons mixture. This suggests that alcohols and oxygenated diluents are most effective in physical

extraction of propionic from dilute solutions. Their hydrogen bond donor ability and high relative permittivity (ε) and ET value

could be suggested as the reason for higher extractions in these diluents.

2. With increase in acid concentration, diluent

DK was found to be nearly constant for alcohols and ketone, however, for aliphatic

and aromatic hydrocarbons there is abrupt increase in diluent

DK values at high acid concentration.

3. Partition (P) and dimerization (D) coefficients were also evaluated. The values of P and D shows a close relation with the

chemical nature of solvent.

4. Extractability of the acid was correlated with the physico-chemical properties of the solvents, yet no general correlation could

be found. The reason for that may be that the effect of diluent is determined by the ratio of the contribution of the solvation of acid

to the free energy of extraction. Z parameter and the ET parameter, which give the assessment of solvation energy of the solute and

show the effect of intramolecular forces better, were found to explain the trend of extraction. ET parameter, whose values could be

successfully obtained for different diluents, was finally employed for the comparison. It is found that higher the ET value of the

solvent higher is thediluent

DK .

5. Effect of temperature on P and D was also studied using different diluents (oleyl alcohol, ethyl acetate, MIBK, 1-decanol and 1-

octanol). For the physical extraction of carboxylic acids using 1-octanol ΔH and ΔS values were calculated as, 5.866 kJ/mol and

27.363 J/mol K. It can be seen that ΔH is positive, thus the partitioning process is endothermic. ΔS value for the extraction of

propionic acid is also positive, thus the partitioning process is entropy driven process and the order of system increases.

REFERENCES

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butylphosphate, tri-n-octylamine and Aliquat 336)”,. Ind. Eng. Chem. Res., Vol. 47, pp. 6192–6196

2. Keshav A, Wasewar K L and Chand S (2008b), “Equilibrium Studies for Extraction of Propionic Acid Using Tri-n-

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